The invention concerns a hydraulic valve system with a supply connection arrangement, having a high-pressure connection and a low-pressure connection, a working connection arrangement, having two working connections, which can be connected with a hydraulic motor, and a directional valve between the supply connection arrangement and the working connection arrangement, which is connected with the working connection arrangement via working lines, in which are arranged check valves, which can be opened by means of pressure.
Such a valve system is known from, for example, DE 199 19 105 C2. In dependence of the desired operation direction, the directional valve controls a path for pressurised hydraulic fluid from the high-pressure connection to one of the two working connections and from the other of the two working connection to the low-pressure connection. If required, also a throttling resistance is influenced by the position of the slide of the directional valve, said throttling resistance determining, together with the pressure ruling over the directional valve, the amount of hydraulic fluid per time unit to the motor.
The use of check valves in the working lines has the advantage that the motor is protected against unintentional movements. In particular, the check valves ensure that external loads cannot move the motor connected to the working connections, unless the operator intentionally influences this. Only when the pressures available in the system open the check valves, a movement of the motor is possible, that is, also with negative loads, when the load has to be lowered.
A problem in this connection is, however, the fact that a supply failure, for example a defect in a pump or in a combustion motor driving a pump, causes that the motor connected to the valve system can no longer be operated at all. When, for example, this motor has lifted a load, it is relatively difficult to find a safe way of returning this load to a position, in which the operating staff is no longer endangered.
The invention is based on the task of avoiding such dangerous situations in connection with supply failures.
In a hydraulic valve system as mentioned above, this task is solved in that a flow control valve is arranged in at least one working line.
By means of the flow control valve, a fluid path from the motor, that is, from a working connection, to the low-pressure connection can be opened intentionally, to enable the lowering of a load. As long as the motor can put pressure on the working connection, the activation of the flow control valve makes it possible to relieve this load, that is, to let fluid flow off from the motor. This makes it possible, for example, to lower loads so much that they are supported on a foundation, and that a pressure generation no longer occurs at the working connection. Thus, the check valves no longer have to be opened to effect such a relief. On the contrary, an additional valve is used, namely the flow control valve.
It is preferred that the flow control valve is activated by means of a handle. Thus, it is not even necessary any longer to produce an additional hydraulic pressure to activate the flow control valve. The flow control valve can be opened by a direct and immediate intervention from the outside.
The handle is in the form of a threaded spindle. By means of a threaded spindle, a very delicate control of the opening movement of the flow control valve is possible. When, for example, a relatively low pitch of the thread of the threaded spindle is chosen, it is possible, by means of a delicate turning of the threaded spindle, to effect a similarly delicate opening of the flow control valve. Particularly with heavy loads, a delicate opening of the flow control valve is extremely advantageous, as this enables lowering of the load at a high accuracy and a low speed in a controlled manner.
The flow control valve is integrated in a pressure relief valve system. Thus, additional component groups can be saved, which should otherwise be arranged in the valve system. In particular, it is not required to establish additional lines, when the valve system already comprises a pressure relief valve system. However, a pressure relief valve is comprised in most hydraulic valve systems anyway, to avoid an overloading of the valve system.
The pressure relief valve system has a valve, which is both pressure-operable as pressure relief valve and manually operable as flow control valve. Thus, only one valve is used, which has, however, two functions, and which can be opened in different ways. On the one side, the valve opens, when the pressure in a pressure chamber gets too high, to effect a pressure relief at an overpressure. In a second function, this valve can, on the other side, also be opened to effect a manual lowering of a load connected to a working connection. In this case, in fact only one additional operation option is required, for example a handle, which acts upon the valve element of the valve to open the valve.
Also, the pressure relief valve system is designed with an integrated anti-cavitation valve. Such a system is known from, for example, DE 196 00 275 A1. The combination of the pressure relief valve with an anti-cavitation valve saves space and simplifies the piping arrangement. When a third function is additionally integrated in this valve, there will be sufficient opportunities of securing the valve system against overpressures on the one side, and of providing safety measures against inoperability of the valve on pressure failure on the other side.
In addition, the pressure relief valve has a valve element, which bears on a valve seat, an auxiliary valve element bearing on an auxiliary valve seat, which is formed in the valve element, the auxiliary valve element being operable from the outside. The auxiliary valve element being operable from the outside thus realises the function of the flow control valve, that is, when the auxiliary valve element is lifted from the auxiliary valve seat, the pressurised hydraulic fluid at the working connection can escape. Usually, this pressure is not sufficient to open the pressure relief valve. When, however, the pressure relief valve is supported by the handle, also lower pressures will be sufficient to lower the load.
It is particularly preferred that the auxiliary valve element is fixed to an operating rod, and is pressed against the valve element by a spring from the side, on which also the valve seat bears, the handle acting upon the auxiliary valve element against the force of the spring via the rod. Compared with the valve known from DE 196 00 275 A1 only slight changes are required. Actually, only a handle must be provided to act upon the rod, on which the auxiliary valve element is fixed. This embodiment is effective and can be realised at relatively low costs.
Further, the handle can be used as a lift limitation for the anti-cavitation valve. The position of the handle thus determines the opening width of the anti-cavitation valve. Thus, for example when controlling a negative load, the feeding speed can be influenced by the anti-cavitation valve, meaning that the pressure relief valve with integrated anti-cavitation and flow control valves gets an additional function.